Many million tons of poultry litter are produced annually in the United States virtually all from intensive systems. Poultry litter is solid waste material composed primarily of bedding material (any of a variety of lignocellulose materials), feathers, spilled animal feed, and poultry excreta, the litter having been removed from poultry houses. The relative proportion of bedding to excreta can vary widely, as can the chemical nature of the litter. There also may be pathogens, weed seed, and drug contaminants present in the litter. Litter is, of course, malodorous due to various odorants or precursors thereof. In addition to free ammonia there have been identified odorants such as mercaptans, sulfides, di-ketones, indole, and skatole. Litter contains and during storage and composting generates many volatile organic compounds (VOCs).
Poultry litter is recognized as a serious source of nitrification of waters. As poultry production steadily grows due to demand for poultry products and population growth; so does the waste from this production. Efforts to protect our environment have led to regulations causing local producer/farmers to struggle with meeting state mandated nutrient management program requirements while remaining solvent with narrow profit margins.
Currently, the U.S. alone generates 13 million tons of poultry litter each year. The growing population consuming more poultry also needs an increasing food supply from crops which require fertilizer. Poultry litter is used as fertilizer due to its well-documented source of primary plant nutrients (nitrogen, phosphorus, and potassium), secondary nutrients (sulfur, magnesium, and calcium), and micronutrients like zinc, copper, iron, boron, nickel, manganese, and molybdenum. However, using poultry litter as a fertilizer in either its raw form or after traditional treatments like composting or rotary drum heat treatment is not nutrient efficient, energy efficient, or safe to our health or environment. Also, even litter that has been heat treated will give off offensive odors when exposed to moisture or rain. Additionally, litter haulers are faced with a growing supply of poultry litter and a narrowing availability for land application. This leads to stockpiles of litter that further cause problems from release of greenhouse gases, potential leaching and run-off, human and animal exposure to pathogens, and loss of nutrients in the litter.
Animal production concentrated in small regions has led to litter disposal problems causing growing health and environmental issues, both internationally and in the U.S. According to the USDA ERS, 69% of the broilers produced in the U.S. were produced in the southern states of Georgia, Arkansas, Alabama, Mississippi, North Carolina, Texas, and Kentucky. Currently, poultry litter management regulations require poultry producers to create nutrient management plans that include safe disposal and use of their litter waste. These regulations put a considerable burden of management on the shoulders of local farmers who already face tough profit margins. Currently, most poultry litter is applied to fields. However, this use of litter is inefficient, bad for the environment, and a threat to human health. Furthermore, farmers face regulations on land application that restrict when litter can be applied. The concentration of litter production to certain regions combined with the regulations on land application have created an excess of litter with no place to apply it. This leads to a need for safe uses of the litter, especially in times when land application is controlled or banned.
One way that poultry litter is a threat to our environment is in land applying it in raw form. This practice has been shown to lead to runoff to waterways and leaching to groundwater leading to nitrification of waterways. This is especially true when phosphorus builds up in the soil due to repeated applications of poultry litter. The leaching of phosphate from the soil is a serious problem in major waterways such as is seen currently in the Chesapeake Bay.
Poultry litter is typically 3-3-3 (% N-% P2O5-% K2O), on average typically contains 20-30% moisture and 25-35% organic carbon. Since plants have a much higher need for nitrogen than for phosphorus, litter is added at higher levels than the plants are able to take up phosphorus. As a result, with repeated applications of litter, phosphorus builds up in the soil which has led to regulations now in place to limit the land application of litter in areas with high phosphorus or areas close to waterways.
Poultry producers often use lime to control disease in their poultry houses. As a result, litter from these producers may be high in calcium. When this litter is applied, calcium levels in the soil increases as well as the soil pH. Over time, this inhibits the uptake of other nutrients such as magnesium and zinc.
Poultry litter poses human health problems in various ways. Untreated litter dust not only smells bad but also carries pathogens in the air that can be dangerous to humans. These pathogens also have potential to be transmitted to livestock feeding on grass in fields treated with litter as well as to vegetables and other crops grown with litter used as fertilizer. Typical methods of mitigating this problem include composting or stacking the litter. These methods allow heat to kill the pathogens before applying.
However, pathogens may persist due to uneven heating during the process and not only survive but become even more virulent than prior to the treatment. Food can then be contaminated when grown with the treated litter.
Another health concern of using litter is the existence of drugs and hormones in the litter. The presence of antibiotics in our environment as well as other drugs has become an increasing concern to human health. Not only can these enter the water supply; but in the case of antibiotics, they can increase the virulence of bacteria in our environment.
Composting and stacking litter has an additional negative effect on our environment which is the release gases and reduced air quality. As stated above, pathogens can be transmitted to air by poultry litter. Composting litter also causes losses of both nitrogen and phosphorus due to denitrification and ammonia volatilization, run-off, and leaching. These losses can be quite high.
Another method of treating poultry litter to create a product for fertilizer is rotary drum drying. This uses heat to kill harmful organisms and heats the product more evenly. However, it requires the use of fossil fuels, is inefficient, and suffers from nutrient loss, in particular nitrogen, as well as the generation of greenhouse gases. Also, when the litter encounters moisture; offensive odors are generated.
Canadian Patent No. 1214062 (Anthony, Smith, and Shirley) discloses a process of producing fertilizer from poultry litter, the complete disclosure of which is incorporated herein by reference. However, this process is limited in the amount of nitrogen in the final fertilizer product. The present invention is a substantial and surprising improvement over this patent.
U.S. Pat. No. 4,650,682 (Shirley, Jr.) illustrates a preferred type of acidifier-ammoniator vessel that can be modified as described herein for use in the present process. The complete disclosure of this patent is incorporated herein by reference.
There is a great need for a clean, non-polluting, poultry litter-based fertilizer that is free of offensive odors and has an increased level of nitrogen. Such a clean poultry litter-based fertilizer would provide benefits to plants due to its nutrient content as well as its ability to improve soil health. Arable land is decreasing and one of the causes of loss of arable land is a depletion in organic carbon. Poultry litter contains organic carbon; and when this litter is land applied, leads to an increase in soil carbon that improves the water holding capacity of soil. Using a clean poultry litter-based fertilizer on land would help to reverse damage from long term cultivation by improving formation of soil aggregates which improves water and oxygen diffusion rates.
Poultry litter is typically comprised of 30% bedding material and 70% excreta. As a result, the litter is a complex mixture of many compounds including sugars, fatty acids, cellulose, lignin and extractives, vitamins, and amino acids. Poultry litter naturally contains all of the nutrients, secondary nutrients, and micronutrients needed by plants including N, P, K, S, Zn, Ca, Mg, Mn, B, and Cu. The nutrient content of litter depends on many factors including management practices, the type of bedding material used, feeds, and more. Typically, on a dry basis poultry litter contains 1%-4% N, 25%-35% carbon, 1.4%-6.6% P2O5, 1.3%-4.1% K2O and 0.3% to 2% S. Poultry litter also contains high levels of lignocellulose due to the bedding materials used in poultry houses. The bedding materials used are readily available forest and agricultural wastes such as straw, wood chips, peanut hulls, and rice hulls, for example. Poultry litter differs significantly from other wastes used to produce fertilizer. Poultry litter contains a multiplicity of organic compounds in addition to lignocellulose and these differ from organic compounds in manures, sewage, and biosolids.
It is well known that ammonium nitrate is explosive. According to the United States Department of Homeland Security, the minimum detonable level of ammonium nitrate is 10% (DHS Ammonium Nitrate Security Program, Vol. 84 No. 106, Fed. Reg. 25495, Jun. 3, 2019).